Recently, Reddit user u/mesonofgib asked the people of r/movies this question: "What's the best film that is NOT faithful to its source material?"
Here was their setup/example:
"We can all name a bunch of movies that take very little from their source material (I Am Legend, World War Z, etc.) and end up being bad movies.
"What are some examples of movies that strayed a long way from their source material but ended up being great films in their own right?
"The example that comes to my mind is Starship Troopers. I remember, shortly after it came out, people I know complaining that it was miles away from the book, but it's one of my absolute favorite films from when I was younger. To be honest, I think these people were possibly just showing off the fact that they knew it was based on a book!"
And here's how everyone else responded:
Warning: Spoilers ahead.
1. "The Fox and the Hound book ends with the hunter shooting the hound in the back of the head as it gently licks him, and the hunter goes off to die alone in a nursing home, irrelevant to society. This is after killing the fox, its mate, and its kits. The animated Disney movie is a genuinely great movie about friendship."

2. "Shrek. I honestly don’t understand why people love the children’s book. It’s pretty straightforward and boring, though the illustrations are cool. The movie takes the basic concept and elevates it 10,000% into something unique and hilarious."

3. "The Bourne trilogy. It takes the first five minutes from Book 1, then goes completely in its own direction and is much better as a result."

4. "Jurassic Park, although aside from changing the genre from outright sci-fi horror to more action-adventure with slight horror elements, I feel the spirit of the novel survives pretty much intact in the movie."

5. "The Shining. One of my favorite movie facts is from The Shining. In the book, the Torrance family drives a red Volkswagen Beetle; in the movie, they drive a yellow one. Later in the movie, as Halloran is driving in the snowstorm, he passes a car accident where a semitruck has crushed a red Beetle. This is thought of as director Stanley Kubrick knowing he totally changed the story and was actively snubbing it with this shot."

6. "Children of Men is very, very different. The book is very good, don't get me wrong, but the movie takes the core concept of mass infertility and goes in a completely different direction with it. Out of the two, I prefer the movie, but the book is well worth the read."

7. "Who Framed Roger Rabbit — similar concept regarding the coexistence of cartoons and humans, vastly different developments."

8. "How to Train Your Dragon, easily. Astrid is a great addition to the cast of characters, for starters. Toothless is far more interesting as the dreaded, mythical Night Fury than the 'newt with wings' that appears in the books. That being said, the films draw extensively from Cressida Cowell's illustrations for the character and creature designs, and it pays off in spades."

9. "The Wizard of Oz books were darker and more twisted than the movie. Like, the Scarecrow murders crows, and the Emerald City is only emerald because you were forced to wear green-tinted glasses."

10. "A lot of the Bond movies have only the book title in common. The movie version of Moonraker is set in Venice, the Amazon rainforest, and outer fucking space! The book takes place in Kent, England."

11. "Jaws. In the book, Hooper has an affair with Brody's wife and dies in the shark cage."

12. "I feel like the Blade Runner novel isn't really comparable to the movie — it's just barely a story. What Ridley Scott did was borrow some elements from it and do his own thing."

13. "Forrest Gump. Book is 180 degrees different, character-wise."

14. "Not the 'best film' by any stretch, but I really enjoyed Constantine. However, aside from the name (which isn't even pronounced the same way) and a vague association with the paranormal, it has pretty much nothing in common with the comics."

15. "Die Hard, which was based on Nothing Lasts Forever by Roderick Thorp...which is a sequel to another novel of his, The Detective."

16. "Stardust. The book is more practical, but the movie is just pure delight."

17. Finally: "Fight Club. Even the author (Chuck Palahniuk) says the movie is better than his book."

Note: Some responses have been edited for length and/or clarity.